A Forest Management Nonpoint Source Risk Assessment 



on the watershed's sensitivity (Coboum 1989). 

 These values are based on research conducted 

 by Hair and others (1975). 



If Howard Creek were in Region 5, its 

 combination of slopes and geology would proba- 

 bly classify it as moderately sensitive, and there- 

 fore would have a "Threshold for Concern" of 

 15 percent. Note in Table I-l that six years of 

 management produced an unrecovered distur- 

 bance of nearly 19 percent. The "yellow flag of 

 caution" would not yet have been raised be- 

 cause of recovery and only some percentage of 

 the disturbance was equivalent road acres. The 

 specialists on the Lolo National Forest raised 

 their own "yellow flag of caution" based on 

 monitoring information. Nevertheless, there 

 were some indications of changes in the system, 

 so perhaps a 10 percent to 15 percent distur- 

 bance threshold is legitimate. 



Similar rationale for assigning a risk index 

 value threshold may be used. A moderate risk 

 for generating cumulative effects has a value of 

 3 in the Erosion-Impact matrix. If we were to 

 chose a 15 percent areal disturbance limit, and 

 be willing to accept moderate risk, then the risk 

 index target would be 0.45 (0.15 X 3). A ten 

 percent disttirbance limit would have a risk 

 index of 0.3. Similarly, acceptance of higher or 

 lower risk could also increase or decrease the 

 target. In either event, the Howard Creek water- 



shed was being stressed, or nearly so, in 1986. 

 Recovery is rapid, however, so deferring activ- 

 ity or selecting low risk options (a combination 

 of sites and methods) would allow the cumula- 

 tive risk value to fall. Note that by 1990, the 

 cumulative risk index value fell to about 0.23. 



Summary 



This methodology has not yet been applied 

 to any watersheds in the Flathead Basin. Care 

 was taken, however, to make sure that all infor- 

 mation required for the procedure is ahieady 

 available on the Flathead National Forest GIS. 

 We see distinct advantages that this risk assess- 

 ment procedure offers over other cumulative 

 effects analyses. First, machine processing of 

 data tends to minimize "human errors." Sec- 

 ondly, the technique allows us to weight our 

 assessment of risk by our understanding of both 

 erosion and peak flow generation processes and 

 the inherent impacts associated with various 

 management activities. 



We strongly recommend testing the proce- 

 dure in the Flathead Basin, using the Flathead 

 National Forest's GIS capability and the data 

 sets obtained for the other watershed analyses 

 conducted by the Cooperative, and comparing 

 the results with those of the other techniques. 



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